Abstract
In this research paper the residual strength of clay is deemed to correspond to the total value of the strength of the soil particles used in the specimen. The frictional force of the soil particles was measured by using Atomic Force Microscope (AFM); then the frictional force and the residual strength of the specimen were compared. The surface profile of the shear surface in residual state, the friction coefficient, the velocity dependency of frictional force and the adsorptive force of clay adsorbed water were measured by AFM in micro area. As a result, although the shear surface appeared flat to the naked eye, it actually turned out to be rough. The increase of the frictional force in micro area was proportional to the increase in the vertical stress, and the increase rate or angle of friction [φ] was very small: less than 5°. The adsorptive force of adsorbed water was 4.1×10^<-2>nN for Kunipia F, 8.9×10^<-1>nN for Kaolin KH from the Force Curve. Since the angle of shear resistance of the specimen in macro [φ'_r]was around 20°, the shear strength of macro and micro were not equal. Even when the micro strength was simply integrated, it didn't equal the macro strength.
